This invention relates, in general, to one shot circuits, and more particularly, to a resettable one shot circuit having noise rejection.
One shot circuits, also called monostable multi-vibrators, are well known and have been used in electronic circuits for a long time. Many digital systems use some kind of a one shot circuit as a delay network for resetting the system. This presettable delay allows the system to stablize during the initial power up time period, therefore allowing the oscillators, clocks, and other signals to be present before normal operation of the system. The one shot circuit can also be used as a small delay for preventing race conditions in digital systems. In addition, there are other applications such as frequency doublers and low pass filters. Some commercially available one shot circuits are MC14528 and MC14538 sold by Motorola, Inc. A highly accurate one shot multi-vibrator, having a large amount of digital circuitry, is disclosed in U.S. Pat. No. 3,768,026 which issued Oct. 23, 1973. The one shot disclosed in this patent uses the output to control a first logic gate thereby gating clock signals into the one shot multivibrator. Such a circuit while highly accurate requires considerable amounts of digital circuitry. Many applicatiohs do not require such a highly accurate one shot but do require a one shot which would consume a smaller amount of silicon area on an integrated circuit.
Accordingly, it is an object of the present invention to provide an improved one shot circuit which is retriggerable and resettable.
Another object of the present invention is to provide a one shot circuit which uses a feedback signal from the output to reject input noise and which operates in an analog fashion.